1. Field of the Invention
The present invention relates to a method for recovering a polymer, more particularly, a method for recovering a polymer efficiently from a polymer solution obtained by a solution polymerization.
2. Description of the Related Art
Generally in order to recover a polymer from a polymer solution obtained by a solution polymerization, the polymer solution after polymerization is washed with water or the like to decompose and remove the residual catalyst and then devolatilized to remove the volatiles such as a polymerization solvent, an unreacted monomer or a small amount of water or the like from the polymer solution, whereby recovering the polymer. In a conventional devolatilization process, a polymer solution is concentrated previously for example by a flash evaporation or the like and then a steam stripping is performed.
However, the method described above poses a steam consumption as problematically large as 70 parts or more by mass per 100 parts by mass of a solvent in spite of an attempt to multiple utilization of the steam generally using several strippers. Accordingly, a devolatilization method employing no steam stripping, including a method using a devolatilizing extruder such as a twin-screw extruder and the like or using a thin film evaporator has been investigated.
While the steam consumption is reduced substantially by using a devolatilizing extruder or a thin film evaporator for a devolatilization, the application to a polymerization solution of an elastomer such as a butadiene rubber or a styrene-butadiene rubber or the like was revealed to pose an additional problem which is described below. Thus, since such elastomer characteristically causes, unlike to an ordinary thermoplastic resin, a rapid increase in the solution viscosity at a higher concentration which is not reduced correspondingly even when the temperature is elevated, a higher concentration established at a later stage of a devolatilization process results in a rapid increase in the power required to be exerted by a devolatilization machine such as an extruder or the like, which leads to a problematically reduced devolatilizing efficiency.
Accordingly, in an attempt to solve this problem, a twin-screw extruder provided with a vent (for example in Japanese Patent Publication No. 47685/1982, Japanese Laid-Open No. 12949/1979) or a devolatilization performed using a devolatilization aid such as water or the like (for example in Japanese Patent Publication No. 442/1988, Japanese Laid-Open No. 91101/1984, Japanese Patent Publication No. 29721/1985, Japanese Patent Publication No. 52163/1986) was proposed. Nevertheless, such attempt resulted in no sufficient devolatilization efficiency.
The present invention overcomes the problems experienced conventionally as described above, and is intended to provide a method for recovering a polymer with sufficient devolatilizing efficiency.
The present invention is based on the findings described above and can be described as follows.
1. A method for recovering a polymer comprising heating a polymer solution obtained by a solution polymerization indirectly in a pipe to evaporate a solvent while forming a gas-liquid mixed phase flow or a gas-liquid-solid mixed phase flow followed by supplying the gas-liquid mixed phase flow or the gas-liquid-solid mixed phase flow into a recovery tank to recover the polymer.
2. A method for recovering a polymer according to 1 above, wherein water or steam is infused into the polymer solution in the pipe.
3. A method for recovering a polymer according to 2 above, wherein the amount of the water infused is 0.001 to 20 parts by mass based on 100 parts by mass as the solvent in the polymer solution.
4. A method for recovering a polymer according to 3 above, wherein the number-average molecular weight of the polymer in the polymer solution is 5,000 to 1,000,000.
5. A method for recovering a polymer according to 4 above, wherein the viscosity of the polymer solution is 0.001 to 300 Paxc2x7s.
6. A method for recovering a polymer according to 5 above, wherein the concentration of the polymer in the polymer solution is 0.1 to 80% by mass.
7. A method for recovering a polymer according to 6 above, wherein the polymer is at least one selected from the group consisting of butadiene rubber, styrene-butadiene rubber, isoprene rubber, ethylene-propyrene rubber, butyl rubber, styrene-butadiene copolymer, styrene-isoprene copolymer, butadiene block polymer, butadiene resin and acryl resin.
8. A method for recovering a polymer according to 7 above, wherein the linear velocity of a gas at the outlet of the pipe is 10 m/s or more.
9. A method for recovering a polymer according to 8 above, wherein the devolatilizing efficiency is 0.6 or less.
10. A method for recovering a polymer according to 2 above, wherein the amount of the steam infused is 0.001 to 30 parts by mass based on 100 parts by mass as the solvent in the polymer solution.
11. A method for recovering a polymer according to 10 above, wherein the number-average molecular weight of the polymer in the polymer solution is 5,000 to 1,000,000.
12. A method for recovering a polymer according to 11 above, wherein the viscosity of the polymer solution is 0.001 to 300 Paxc2x7s.
13. A method for recovering a polymer according to 12 above, wherein the concentration of the polymer in the polymer solution is 0.1 to 80% by mass.
14. A method for recovering a polymer according to 13 above, wherein the polymer is at least one selected from the group consisting of butadiene rubber, styrene-butadiene rubber, isoprene rubber, ethylene-propyrene rubber, butyl rubber, styrene-butadiene copolymer, styrene-isoprene copolymer, butadiene block polymer, butadiene resin and acryl resin.
15. A method for recovering a polymer according to 14 above, wherein the linear velocity of a gas at the outlet of the pipe is 10 m/s or more.
16. A method for recovering a polymer according to 15 above, wherein the devolatilizing efficiency is 0.6 or less.
17. A method for recovering a polymer according to 1 above, wherein further removing a residual solvent by supplying the polymer in the recovery tank to a devolatilizing extruder and molding of the desolvated polymer.
18. A method for recovering a polymer according to 17 above, wherein water or steam is infused into the polymer solution in the pipe.
According to the invention, the polymer can efficiently be recovered without changing the physical characteristics or the chemical characteristics of the polymer. Especially when recovering a polymer from a polymer solution having a high viscosity, an infusion of water or steam serves to reduce the viscosity of the polymer solution and also to increase the flow rate in the pipe, whereby ensuring the prevention of the occlusion of a pipe and facilitating the operation. In addition, a substantial reduction in the steam consumption allows the operation to be accomplished at a lower cost.
A method for recovering a polymer of the invention comprises heating a polymer solution obtained by a solution polymerization indirectly in a pipe to evaporate a solvent while forming a gas-liquid mixed phase flow or a gas-liquid-solid mixed phase flow followed by supplying the mixture to a recovery tank to recover the polymer.
Water or steam also may be infused into a polymer solution in a pipe.
A polymer to which a method of the invention is applied may not be limited particularly as long as it is a polymer capable of being synthesized by a known solution polymerization. With regard to the preferable physical parameters of a polymer which can efficiently be recovered, the number-average molecular weight Mn is preferably 5,000 to 1,000,000, more preferably 20,000 to 800,000 and most preferably 50,000 to 500,000, and the viscosity of the polymer solution supplied is preferably 0.001 to 300 Paxc2x7s, more preferably 0.005 to 200 Paxc2x7s and most preferably 0.01 to 100 Paxc2x7s. As a polymer there may be mentioned butadiene rubber, styrene-butadiene rubber, isoprene rubber, ethylene-propylene rubber, butyl rubber, styrene-butadiene copolymer, styrene-isoprene copolymer, butadiene block polymer, butadiene resin, acrylic resin and the like. For an efficient operation without any occlusion of the pipe, the concentration of a polymer supplied is preferably 0.1 to 80% by mass, more preferably 1 to 50% by mass, most preferably 5 to 30% by mass.
Solvent used in the invention is not particularly restricted but may be toluene, xylene, n-hexane, cyclohexane, n-pentane, cyclopentane, iso pentane, n-heptane, cycloheptane, noctane, cyclooctane, n-decane, benzene dichloromethane and the like which is used in solution polymerization.